Time Scales Steered by Optical Clocks

Abstract

Although optical frequency standards made rapid progress these days, microwave standards are still employed as source oscillators of time scales because an oscillator free from phase jumps is a prerequisite. Currently, for high-end users such as national metrology laboratories, hydrogen masers (H-masers) have adequate balance of the stability and reliability. Thus, optical clocks may play the role of the standards to which the time scales refer to in order to adjust their scale intervals. The benefit of using optical frequency standards, in this case, would be the capability to evaluate the scale interval of the H-maser more quickly. To investigate such possibilities of “optical” steering, we evaluated the behavior of an H-maser over a few months with reference to a ⁸⁷Sr lattice clock. The evaluations clearly demonstrated a stable linear drift of the H-maser frequency, indicating the capability of compensating the drift for a stable time scale. This prospect was also supported by a numerical simulation based on the record of H-maser-UTC(NICT)-UTC link.